Recently, as described in WO 2011/086695 corresponding to US 2012/0274277 A1, a hybrid vehicle having a plug-in function for executing a charging operation of a high voltage battery using an external battery charging facility has been developed. When the hybrid vehicle has the plug-in function, it is necessary to activate an electronic control device (or electronic control unit, ECU) so that the plug-in function is executed under a condition that a main switch such as an ignition switch of the vehicle is in an off state.
Accordingly, in a construction described in WO 2011/086695, a plug-in ECU (i.e., PLG-ECU) for controlling the battery charging device is activated by a pilot signal output from the external battery charging facility. The battery charging device converts an alternating current electricity of the external battery charging facility to the charging electricity for charging the high voltage battery. When the plug-in ECU is activated, the plug-in ECU outputs a wake-up signal to the hybrid ECU (i.e., HV-ECU), which executes a charging and discharging control operation of the high voltage battery. Thus, when the plug-in ECU and the hybrid ECU are activated, the charging process of the high voltage battery is executed using the power source of the external battery charging facility.
The hybrid vehicle having the plug-in function is in an early phase of diffusion. Thus, the hybrid vehicle without the plug-in function is still major. Accordingly, for example, it is necessary to prepare both the hybrid ECU having the plug-in function as an additional function and the hybrid ECU having the fundamental function without the plug-in function independently for the hybrid vehicle. In this case, since two types of the hybrid ECUs are prepared, if a circuit board made of a printed circuit board, on which various electronic elements and circuits are mounted, for the hybrid ECU having the plug-in function is developed independently from the hybrid ECU having the fundamental function only, the cost of development is necessary for each hybrid ECU.
Here, when the hybrid ECU having the plug-in function is compared with the hybrid ECU having the fundamental function only, the fundamental functions of both ECUs have many common parts. Accordingly, it may be possible to share a circuit board with each hybrid ECU. If the circuit board is commonly used in each hybrid ECU, the development cost of both ECUs is much reduced. Thus, the product cost is also reduced.
However, when the additional function of the plug-in function is added to the common circuit board, it is necessary to add a bypass capacitor, for example. Thus, it may be necessary to redesign a regulator and a control circuit for the regulator, which provide the power source circuit. The existence and non-existence of the bypass capacitor much affects a phase margin of the power source circuit. In some cases, at output of the power source circuit may oscillate. Accordingly, it is important to use a method without adding and removing a bypass capacitor when the circuit board is commonly used in each hybrid ECU.
The above issue is not limited to the hybrid ECU. The similar issue arises when a ECU having only a fundamental function and another ECU having a fundamental function and an additional function are independently developed.